Katy Perry says she's pushing back the start of her new tour because of "unavoidable production delays."

Due to the delays. the Philadelphia show date for Katy Perry's "Witness: The Tour" has been rescheduled for Thursday, October 12 at the Wells Fargo Center.

Wells Fargo Center officials say all tickets purchased for the original concert date of September 18 will be honored for the new date. They say refunds are available at point of purchase.

The pop star's "Witness: The Tour" will now begin Sept. 19 in Montreal. Perry said in a statement Thursday that "major elements of my tour stage design could not be available for me to rehearse on until this week."

The tour was originally planned to kick off Sept. 7 in Columbus, Ohio.

Perry said that she's "sorry for any inconvenience this causes."

The singer also announced that Carly Rae Jepsen, Noah Cyrus and Purity Ring will open for her on the road.